Merriam-Webster is going to have to update the next edition of its dictionary, at least if marriage redefiners have their way. Do you know what the words “monogamish,” “throuple,” and “wedlease” mean? If not, you soon will. After all, the power to redefine words is the power to redefine reality.

Let’s start with “monogamish,” a play on “monogamous.” A 2011 New York Times profile of gay activist Dan Savage, headlined “Married, with Infidelities,” introduced Americans to “monogamish” relationships — in which partners would allow sexual infidelity provided there were honest admissions of it.

The “monogamish” perspective is one of the purported ways in which redefining marriage to include same-sex relationships would make marriage better. The article explained: “Savage says a more flexible attitude within marriage may be just what the straight community needs.” After all, the story added, sexual exclusivity “gives people unrealistic expectations of themselves and their partners.”

If a marriage can be sexually open, why should it be limited to two people in the first place? Meet the word “throuple,” which is similar to “couple” but with three people. The word popped up in a 2012 article in New York Magazine that described a specific “throuple” this way:

Their throuplehood is more or less a permanent domestic arrangement. The three men work together, raise dogs together, sleep together, miss one another, collect art together, travel together, bring each other glasses of water, and, in general, exemplify a modern, adult relationship.

More or less permanent. Indeed, some activists come down in favor of “less.” Consider “wedlease,” a term introduced in early August in an op-ed in the Washington Post. Why should marriage be permanent when so little else in life is? Why not have temporary marriage licenses, as with other contracts? “Why don’t we borrow from real estate and create a marital lease?” the author writes. “Instead of wedlock, a ‘wedlease.’” He continues:

Here’s how a marital lease could work: Two people commit themselves to marriage for a period of years — one year, five years, ten years, whatever term suits them. The marital lease could be renewed at the end of the term however many times a couple likes. . . . The messiness of divorce is avoided and the end can be as simple as vacating a rental unit.

Examples can be multiplied. In July, Washingtonian magazine ran a story about “polyamory” headlined “Married, But Not Exclusive.” The article tells us that “the word means ‘many loves’” and that, “as in most major cities, Washington’s polyamorous community is tight-knit.”

The liberal online journal Salon in early August posted a woman’s account of her shared life with a husband, boyfriend, and daughter, under the headline “My Two Husbands.” The subhead: “Everyone wants to know how my polyamorous family works. You’d be surprised how normal we really are.” The author writes: “As far back as I can remember, I felt that loving one person romantically did not preclude the possibility of loving another at the same time. It seemed natural and intuitive to me.”

So, what’s wrong with these trends? Whatever we may think about the morality of sexually open marriages, or multi-partner marriages, or by-design-temporary marriages, the social costs will run high.

If a man doesn’t commit to a woman in a permanent and exclusive relationship, the likelihood of creating fatherless children and fragmented families increases. The more sexual partners a man has, and the shorter-lived those relationships are, the greater the chance he creates children with multiple women. His attention and resources thus divided, a long line of consequences unfold for both mother and child.

At its most basic level, marriage is about attaching a man and a woman to each other as husband and wife to be father and mother to any children their sexual union produces. When a baby is born, there is always a mother nearby: That is a fact of reproductive biology. The question is whether a father will be involved in the life of that child and, if so, for how long. Marriage increases the odds that a man will be committed to the children whom he helps create and to the woman with whom he does so.

Marriage, rightly understood, brings together the two halves of humanity (male and female) in a monogamous relationship. Through vows of permanence and exclusivity, husband and wife pledge to each other to be faithful. Marriage gives to children a relationship with the man and the woman who made them, their mom and dad.

But ideas and behaviors have consequences.

The breakdown of the marriage culture since the 1960s made it possible in this generation to consider redefining marriage in the law to exclude sexual complementarity. But if the law redefines marriage to say the male-female aspect is arbitrary, what principle will be left to retain monogamy, or sexual exclusivity, or the expectation of permanency?

What these new words and redefinitions have in common is that they make marriage primarily about adult desire, primarily an intense emotional relationship between (or among) consenting adults, regardless of size or shape. And why should relationships among consenting adults be exclusive? Or permanent?

If justice demands redefining marriage to include the same-sex couple, will some argue that it demands including the throuple? Or the wedlease? Love equals love, after all.

Ideas once whispered only in obscure academic journals now secure prominent billing in mainstream outlets. But if we redefine marriage to say that men and women are interchangeable, that monogamish relationships are just as good as (better than?) monogamous relationships, that throuples are the same as couples, and that wedlease is preferable to wedlock, then we’ll witness more broken homes and broken hearts.